Introduction

Principle

When SoC boot up, The boot rom will read firmware from boot media(used to be eMMC, SPI, Nand, SD card etc). The boot rom automatically go to maskrom mode when it can not read anything from boot media or boot loader corrupted. In maskrom mode, The boot rom will talk to host PC with Rockusb Protocol over USB cable.

Use maskrom key

The maskrom key in hardware design just short the clock of boot media to ground. Which make boot rom can't read firmware from boot media. Three step to enter maskrom mode with maskrom key. If you don't have a maskrom key on your board. Just replace the maskrom key with "short the clock of boot media to ground".

Long press MASKROM key(no release). This step short the clock of boot media to ground which will make boot rom can not read any thing from boot media. Please refer to here for the MASKROM key on Kylin board.